Expression of ribosomal protein S5 cloned gene during differentiation and apoptosis in murine erythroleukemia (MEL) cells

Murine erythroleukemia (MEL) tells have been used as a suitable model syste m for studying cellular and molecular mechanisms of erythroid differentiati on. In an effort to isolate and characterize genes whose expression change during differentiation. we cloned and sequenced a cDNA of 715 bp (rpS5) fro m a MEL cDNA library. The cloned mouse cDNA showed significant degree of st ructural homology in both DNA and protein level to known human and rat gene s that encode the S5 proteins of 40S ribosomal subunit. The use of 715-bp c DNA as probe revealed the presence of an RNA transcript in the cytoplasm of MEL and human neuroectodermal RD/TE-671 cells. The steady-state accumulati on level of this RNA transcript decreased upon induction of differentiation of both cell lines by treatment with DMSO and UDP-4, two structurally diff erent inducers. Blockade of MEL cell differentiation by the inhibitor N-6-m ethyladenosine presented the constitutive expression of the rpS5 gene. DNA methylation analysis at CCGG sites located at the rpS5 gene locus in undiff erentiated and differentiated MEL cells revealed that the suppression of th e rpS5 gene during MEL cell differentiation is not related to any change in methylation at these sites, Moreover, the rpS5 gene continued to be expres sed in cells undergoing serum-deprived apoptosis, like in control untreated cells. Therefore, we conclude that there maybe a disparate pattern of expr ession of the rpS5 gene in differentiating and apoptotic cells. These data can be valuable in understanding thr role of ribosomal proteins during diff erentiation and cell death (apoptosis) of neoplastic cells, although there is no experimental evidence that the suppression of the rpS5 gene is relate d mechanistically to the induction of differentiation. It may well be consi dered as part of the differentiation process.